Oral Radiology Fall 2005 D1 Study Guide

1. In non- ionizing radiation what is the cutoff amount of nrg for no tissue damage?Radiation less than 13.6 eV

2. Define ionizing radiation?Process of removing or adding an e- to a neutral atom.

3. Define and give 3 examples of particulate radiation?Electrically charged particles that travel in str8 lines @ hi speeds. Alpha, beta,

and cathode rays.

4. What is a beta particle? Is it more penetrating than alpha particles?Negatively charged and emitted from nucleus of radioactive atom. Yes.

5. What is a cathode ray and from where are they produced?Electrons. Produced by manufactured devices (filament of xray tube).

6. Is electromagnetic radiation (EM) ionizing or non-ionizing? Define it and how is it measured?

Ionizing; nrg propagated thru space accompanied by electric and magnetic force fields. Electron volts.

7. Name and describe the 2 concepts of EM radiation?1. Wave concept: oscillating electric and magnetic fields.2. Particle concept: bundles of nrg (photons)

8. Describe gamma rays and xrays?1. gamma rays – emitted from the nucleus of a radionuclide (atom undergoing radioactive decay).2. xrays – produced by interx of e-s w/ outer shell and atoms w/in the e- orbital system of the atom.

9. What are the 13 properties of xrays?a. Pure nrg h. can penetrate matterb. invisible i. differentially absorbedc. no mass j. can produced image on filmd. no charge k. cause fluorescencee. travel @ lite speed l. causes ionizationf. short wavelengths of variable range m. produces biological changesg. travel in str8 lines

18. Q. In what is The X-ray tube sealed? A. An evacuated glass envelope.

19. Q. The cathode is the positive terminal of the xray tube. T or F?

A. False, it is negative.

20. Q. What are the 2 components of the cathode? A. Filament and Focusing cup.

21. Q. What is the filament made of? And what is its function? How is it heated and controlled?

A. Tungsten wire. Source of electrons. Heated by low-voltage circuit, controlled by mA selector and step-down transformer.

22. Q. Define thermionic emission? A. Process of releasing electrons from outer orbits of tungsten atoms.

23. Q. What is the focusing cup made of? And its function?A. Molybdenum. Directs the e-‘s to a certain area on the target of the anode.

24. Q. How do you achieve propulsion of e-‘s toward the anode?A. apply a high voltage difference btw/ cathode and anode (via autotransformer and step-up transformer).

25. Q. What are the components of the anode? Functions of the anode?A. Target, Focal point (found on the tungsten target), Copper stem. Electrical conduction, mechanical support, thermal conduction, x-ray production.

26. Q. What is the Target made of and why this mat’l is beneficial?A. Tungsten. High atomic number, hi m.p., low vapor pressure.

27. Q. Function of focal spot?A. where e-‘s are directed from the filament.

28. Q. What is the significance of a smaller focal spot?a. Sharper the radiographic image.

29. q. Define the Benson line focus principle? And another advantage of this design?a. the effective focal spot is smaller than the actual focal spot due to angulation of the target w/ respect to the cathode. Heat dissipation.

30. q. Describe the heel effect?a. intensity of the xray beam produced at the focal spot is not uniform throughout. There is more intensity on the side of the beam closer to the cathode. Some of the photons produced more nearly parallel to the surface of the angled target will be absorbed by the target itself.

31. q. What is the function of the copper stem?a. holds the tungsten target, dissipates heat from the target.

32. q. Where are stationary anodes used?a. in dental xray machines.

33. q. Where are rotating anodes used?a. larger medical xray machines.

34. q. How does a rotating anode work and what is its benefit?a. Tungsten target rotates during e- bombardment; reduces overheating of target.

35. q. Define rectification?a. Process of converting alternating voltage(AC) into direct voltage(DC).

36. q. What kind of rectification is used in dental xray machines?a. Self-rectification.

37. q. Define self-rectification?a. The potential between cathode and anode changes from positive to negative 60 times each second.

38. q. Define half-wave rectification?a. A type of self-wave rectification where electrons flow from the negative cathode only during the positive half of the AC curve (radiation made only during positive half).

39. q. Define full-wave rectification and in what machines is it used?a. Cathode is always negative using the full potential of the alternating voltage(AC); used in medical xray machines.

40. q. Are half-wave rectifiers efficient?a. No, newer machines are more efficient.

41. q. Give and compare the various types of exposure timers?a. 1. Mechanical – inaccurate 2. Synchronous – limited 3. Electronic – accurate

42. q. Give and define 2 factors used to rate an xray machine?a. 1. Tube rating: The number of seconds that the tube can be energized (How long a machine can be on and produce/make radiation). 2. Duty Cycle: Interval btw/ successive exposures to allow for heat dissipation (Frequency between exposures/recuperation time).

43. q. What are the 2 types of rxn’s (kinetic nrg of e-‘s that move from filament to anode is converted to xradiation)?a. Bremsstrahlung radiation and Characteristic radiation.

44. q. How is Bremsstrahlung radiation produced?a. Occurs when an e- (propelled from filament) passes near nucleus of a tungsten (target) atom → Electron attracted to positive charge of nucleus, → deflected from its original direction, → loss of electrons kinetic nrg which is emitted in form of photon.

45. q. T or F, bremsstrahlung radiation generates photons with a continous wavelength of nrg?True.

46. q. How is Characteristic radiation produced and in terms of the amount of energy what is necessary for xrays to be produced?a. E- (propelled from filament) ejects e- from inner orbits (K or L usually) of the tungsten (target) atom. Ejection of inner orbit e-, amount of nrg supplied to the inner orbital e- must exceed its binding nrg; → e- from outer orbit occupies empty inner orbit space giving off nrg btw/ the 2 shells.

49. q. What level of kVp is required to produce Characteristic radiation?a. kVp greater than 70.

48. q. Which radiation (Bremsstrahlung or Characteristic) accounts for a large % of the interactions at the target?a. Bremsstrahlung.

49. q. What is intensity of the xray beam?a. Quality and quantity.

50. q. How does exposure time affect intensity of the beam and what is the key amount of impulses that occur in a dental xray machine to remember?a. Affects the amount of xrays produced. 60 impulses/second.

51. q. How long is a radiographic exposure that is labeled 30 impulses?a. 60imp/sec x Time = 30 impulses Time = .5 seconds

52. q. How does tube current affect intensity of the beam?a. Also known as mA(milliampere) Affects the # of e-‘s emitted by the cathode → affects the # of xrays made.

53. q. Define mAs?a. milliampere – seconds = mA x sec

54. q. At 15mA and 24 impulses, the mAs = 360. If 10 mA is to be used, what should the exposure time be to maintain the same beam intensity (film density)?a. 15mA x 24imp = 10mA x Exposure time Exposure time = 36 impulses

55. q. How does Tube Voltage (kVp) affect intensity of the beam?a. Quality : maximum energy of the xrays produced. Quantity of xrays produced.

56. q. Define hard and soft xrays?a. hard xray: more penetrating; soft xray: less penetrating xrays

57. q. What is characteristic of the high kVp range and give the range?a. 85-100 kVp; hi nrg, hi freq., short wavelengths, hard xrays. 58. q. Same question for low kVp range?a. 55-65 kVp; lo nrg, lo freq., longer wavelengths, soft xrays.

59. q. Define HVL?a. half-value layer = thickness of absorbing material (Al or Cu) that reduces the xray intensity to ½ its original value. Can be used to express quality of beam.

60. q. Define filtration and how it affects intensity?a. process of shaping xray beam to increase ratio of useful photons. Removes lower nrg radiations produced at the target before the beam reaches the patient.

61. Define inherent filtration? Added filtration?a. Inherent filtration: xray tube and its housing. Added filtration: sheets of Al placed in path of beam.

63. What is total filtration?a. inherent + added filtration.

64. How thick should aluminum filter be for xray machines producing kVp up to 70kVp? And for greater than 70kVp?a. 1.5mm Al; 2.5mm Al.

65. How does Collimation affect beam intensity? Advantages of collimation?a. Restricts size and shape of xray beam. Decreases volume of tissue (patient) irradiated & Improves image clarity by reducing scatter radiation.

66. What is a diaphragm collimator?a. radiopaque material (lead) at opening of tube head.

67. What is PID and which is preferred for most intraoral radiographs: conical, tubular, or rectangular?PID = position indicating device (type of collimator); rectangular preferred.

68. Define and describe how the Inverse Square Law affects beam intensity?

a. Radiation intensity inversely proportional to square of the distance from source. The same amount of radiation covers a larger area at longer distances (therefore less intense than at shorter distance).

69. What is the Inverse square law formula?a. I1 = (D2) 2 I2 = (D1)2

70. If the source to film distance is increased from 8 to 16 inches, what can we say about original beam intensity relative to the new intensity?a. (16)2/(8)2; The original beam was four times as intense.

71. T or F amount of exposure time is directly proportional to intensity of beam?a. True.

72. T or F exposure time is directly proportional to cross-sectional area of beam?a. True.

73. T or F exposure time is directly proportional to distance from source?a. True.

74. Give the formula that relates exposure time (and mAs) to distance from the source?a. Original exposure time (or mAs) = (Original source-film distance) 2 New exposure time (or mAs) = (New source-film distance)2

75. If source-film distance changes from 8 to 16 inches, what change in exposure time needed to maintain same film density? (mA and kVp will remain constant). The exposure time used w/ the 8 inch distance is 6 impulses.a. 6 imp = (8) 2

?? = (16)2

Answer : 24 impulses

76. A dentist uses these factors to make a radiograph: FFD = 8 inches; kVp = 65; mA = 10; time = 0.75 second. Changing to a long-cone technique (FFD = 16 inches) and employing 15mA. What would be his new exposure time?a. 10 mA x 0.75 sec = (8 inches) 2 15 mA x ??????? = (8 inches)2

Answer: 2 seconds

77. Radiation output of a machine at a 16 inch source-film distance is 250mR per second. Under identical exposure conditions, the source-film distance is changed to 12 inches, what will be the new output per second?a.I1 = (D2) 2 I2 = (D1)2

250 mR = (12) 2 ?? = (16)2

Answer: 444 mR

78. Describe the 3 ways xrays interact w/ matter?a. 1. No interaction – passes through patient w/ no interaction w/ tissue atoms. 2. Absorption – xrays completely absorbed by patient. 3. Scattering – xrays deflected in various directions adding to “noise” (film fog) to film instead of useful info.

79. Describe coherent scattering?a. absorption of radiation → causes vibration of atom → radiation emitted. Only type of interaction that doesn’t cause ionization.

80. Describe photoelectric effect?a. Type of scattering where incident photon strikes and ejects an atom’s K-shell electron → producing a photoelectron (negative ion). → Incident photon absorbed by patient. → An outer orbit electron drops into empty K shell, → giving off energy as an xray photon.

81. Describe Compton scattering?a. Incident xray photon strikes and ejects an outer–shell e- → the photon changes direction as scatter radiation ( but retains much of its original nrg) → ion pair produced (negative or recoil e- and a positive atom) → scattered photon and recoil e- can continue to produce other interx.

82. What is defined by this type of radiation measurement: used to measure capacity of radiation to ionize air? SI and traditional units?a. Exposure; SI: Coulomb(C)/kg; Traditional: Roentgen (R)

83. Define Absorbed dose? SI and traditional units?a. used to measure nrg imparted to mass by ionizing radiation. SI: gray (gy); Traditional: rad (radiation absorbed dose)

84. What is equivalent dose? SI and traditional units?a. Calculation used to compare biological effects of different types of radiation. SI: Sievert (Sv); Traditional: rem (roentgen equivalent man)

85. What is Effective Dose (E)? SI and traditional units?a. calculation to estimate risk of radiation damage to tissues. SI: Sv; Traditonal: rem

RADIATION BIOLOGY

1. Define Direct effects of radiation on molecules?a. xray beam interx w/ molecules → ionization of molecules (by photoelectric effect and Compton scattering).

2. What are possible results of molecules in response to direct effects?a. break molecules to smaller pieces; disruption of molec. Bonds; formation of new bonds w/in or btw/ molecules.

3. Define indirect effects of radiation on molecules?a. ionized molecule interx w/ another molecule that was untouched by the xray beam altering the previously unaffected molecule.

4. What is the main mechanism of indirect effects on surrounding previously unaffected molecules?a. Most commonly occurs from irradiated water → production of free radicals → free radical e- transferred to nearby molecules.

5. Which accounts for most of radiation damage? Direct or indirect?a. Indirect

6. Describe the Law of Bergonie and Tribondeau?a. hi mitotic rate; undergo many divisions over time; primitive or immature in differentiation (poorly differentiated).

7. Which cells are more susceptible to radiation damage? Mitotic cells or stable cells?a. Cells undergoing mitosis are more susceptible.

8. Label this Cell survival curve. What does it illustrate and label the axes?

a. A: DQ; B: n C: DO

illustrates the number of cells that are alive following irradiation. X-axis: Radiation Dose. Y-axis: Proportion of surviving cells.

9. In the curve what does n represent?

B

C

A

0.1

0.01

0.001

1.0 0.1

0.37

a. n = shoulder of curve (shoulder = area of no to low damage)

10. In the curve what does DQ represent?a. quasithreshold dose = dose below which very few cells die (safe dose).

11. What about DO?a. DO = D37 = dose which reduces the number of surviving cells to 37% (Slope or cell sensitivity also).

12. What about LD50/30? a. LD50/30 = Dose that kills half of the population in 30 days.

Factors that affect radiation response in tissues

13. List them (factors that affect radiation response in tissues)?a. 1. Dose 7. age of organism

2. RBE (relative biological effectiveness) 8. sex3. Dose or fractionation 9. Tissue volume4. Repopulation 10. Cell differentiation5. OER (oxygen enhancement ratio)6. Chemical modifiers

14. What is RBE used to calculate and give the formula?a. Relative Biological effectiveness = to compare dose of 2 types of radiation to produce same effect;RBE = dose of standard radiation to produce specified biological effect

Dose of test radiation to produce specified biological effect

15. Define linear energy transfer (LET)?a. measure of the rate at which nrg is transferred from the radiation to the tissues.

16. Define fractionation?a. Basis of radiation therapy where dose is divided into equal parts → delivered over time → reduced biological effectiveness of the total dose due to the cells ability to recover from radiation.

17. Define repopulation?a. increase in cell growth, when radiation dose prolonged over time (radiation therapy).

18. Define OER?a. oxygen enhancement ratio = ratio of dose needed to produce particular effect in hypoxic cells : to the dose required to produce same effect in oxygenated cells.

19. T or F increase oxygen content results in decreased radiation damage?a. False, it is directly proportional; increased oxygen results in increased radiation damage.

20. Rank these tissues by their relative radiosensitivity ( put in correct place Highest, High, Intermediate, Low, Lowest)?Growing cartilage/bone, mature cartilage/bone, kidney, muscle, nerves, CNS, liver, skin, cornea, lymphoid tissue, GI tract, bone marrow, gonads, intestinal epithelium, connective tissue, fine vasculature, adult thyroid, salivary gland.a. Highest = bone marrow, intestinal epith, gonads, lymphoid tissue. High = GI tract (including oral mucosa), cornea, skin Intermediate = conn. Tiss., fine vasculature, growing cart/boner. Low = mature cartilage and boner, kidney, liver, adult thyroid, salivary gland. Lowest = muscle, nerves, CNS.

Another way to see the big picture:Sensitive: Spematogonia, Lymphocytes, Hematopoeitic tissue.Less Sensitive: Epithelium, Epidermis.Resistant: CNS, Muscle, Bone.

21. Define acute radiation syndrome?a. collection of signs and symptoms experienced by individuals after whole-body radiation exposure.

Periods of acute radiation syndrome

22. What period and symptoms associated w/ 1- 2 Gy of exposure and onset time?a. Prodromal period; minutes to hours after exposure; anorexia, nausea, vomiting, diarrhea, weakness, fatigue (like flu).

23. What is the latent period?a. symptom free interval.

24. Is 5 or more Gy of radiation supralethal or sublethal? Give the dose that signifies the other and how long also.Greater than 5 → supralehtal (hours to days)Less than 2 → sublethal (few weeks)

25. Several weeks after exposure to 5 Gy. Time to onset and Name the period and its characteristics?a. Hematopoietic syndrome; several weeks after exposure; effects on blood-forming organs → infection, hemorrhage, anemia.

26. What syndrome occurs due to 7-15 Gy exposure and onset?a. Gastrointestinal syndrome; occurs days after exposure → death w/in 2 weeks.

27. If given 50 Gy or greater exposure?a. Cardiovascular and CNS syndrome hours after exposure; death in 1-2 days

28. What are acute effects of lower nrg radiation (< 50 eV)?a. DEEPS : Dermatitis (radiation); Epilation; Erythema; Pigmentation; Skin ulceration.

29. What 2 terms describe late effects of radiation? Describe them?a. Stochastic = random (i.e. genetic mutation); Probability of effect occurring is dose related. Deterministic = Nonstochastic (i.e. radiation induced cataracts); Severity of effect is dose related.

30. Which has a threshold dose which does not? a. Stochastic has no threshold dose, and likewise Nonstochastic has a threshold of dose.

31. Is there a threshold dose of radiation that can cause genetic mutation?a. NO

32. What scientific evidence do we have of radiation effects?a. 1. increased incidence of thyroid cancer – refugee children treated for ringworm;

infants irradiated to reduce thymus gland size.2. increased breast cancer - women treated for mastitis; patients treated for ankylosing spondilitis; TB patients who had several fluoroscopic exams.3. Japanese A bomb survivors4. Radiologists

33. How does radiation affect the genetic pool?a. it only increases the frequencies of the same mutation that already occur spontaneously or naturally in species. (Stochastic – increase dose → increase Chance of mutation).

34. Define doubling dose? What is estimated human doubling dose?a. Doubling dose = dose needed to double the spontaneous mutation incidence); For humans → 1 Gy (100 rads).

35. What do effects of radiation on embryo and fetus primarily depend upon?a. Dose and Stage of gestation.

36. How can radiation affect the embryo/fetus in 1. preimplantation period 2. post-implantation period?a. 1. radiation effect is all or none (death or survival). 2. Microcephaly, CNS defects, Growth retardation, cancer in childhood.

37. How much radiation is safe for a fetus?a. Maximum permissible dose to fetus during gestation = 5 mSv (0.5 Sv). Or “cut –off” point of expected radiation injury = 0.1 Gy (10 rad) dose.

38. Describe effects of therapeutic doses of radiation on oral mucous membrane.a. mucositis; Candidiasis; tissue remain atrophic after healing.

39. What about to Taste buds?a. decreased taste acuity after 2-3 weeks of radiotherapy; nearly normal at 2-4 months post Tx.

40. What about to the salivary glands?a. decreased flow, increased viscosity → leads to xerostomia; increased acidity/decreased buffer cap. → greater risk of caries;

41. What about to the teeth?a. developing teeth fail to develop completely or delayed eruption; Fully formed erupted teeth are not affected; 42. What about Bone?a. 1. damage to vasc. Supply and decrease in osteoblast/clast cells

2. Mandible more severely affected than Maxilla (lack of anastymosis)3. susceptible to infection and necrosis remains indefinitely following Tx.4. Osteoradionecrosis (type of osteomyelitis).

HEALTH PHYSICS 1. What are sources of natural radiation? a. External sources: Outer space cosmic radiation and Terrestrial source from soil. Internal sources: Ingested food/water and inhaled (greatest 56%).

2. What is approximate avg. dose for natural radiation in the U.S.? a. 0.6 mSv/yr

3. What is the largest source of artificial radiation?a. Medical and Dental.

4. How can you compare the risk of various types of radiation exposure?a. Use Effective Dose Equivalent (HE) which is measured in rem and Sv

5. Define effective dose equivalent?a. weighted sum of the equivalent doses to each of the tissues of the body exposed.

6. Define Critical Organ Concept? a. Certain organs of the body possess the potential to significantly detract from the quality of life of individuals in whom they are irradiated.

7. What are critical organs exposed during dental radiography?a. Female breast, skin, thyroid, lens of eye, bone marrow and other hematopoietic tissue, gonads. ?????????

8. Define ALARA?a. ALARA = as low as reasonably achievable. The amount of radiation exposure must be kept to a minimum. (b/c we want to avoid biological effects).

9. What is the maximum permissible dose (MPD)?a. max dose that would not be expected to produce any significant effects in a lifetime.

10. MPD for occupationally exposed persons? Non-occupationally exposed persons?a. 50 mSv; 5 mSv

11. T or F radiation from diagnostic exposure is separate from MPD for non-occup. ppl?a. True, but the actual radiation dose is hard to measure.

12. What can be use to measure internal doses then?a. phantoms w/ thermoluminescent dosimeters (tld’s); to measure skin entrance doses.

What steps should be taken to reduce radiation exposure in dental radiography?On exam : Anything that protects your patient will protect you.

1. Intraoral procedures what type film preferred?a. E-speed (ektaspeed).

2. Intraoral film is nonscreen or screen film?a. nonscreen.

3. For extraoral procedures what film is preferred?a. film that works best w/ rare earth intensifying screens.

4. Source-to-film distance should be?a. as great as possible to decrease dosage and increase sharpness.

5. Collimation should be?a. as close to size of film as possible → prefer rect. cone.

6. Now list the rest?a. 1. filtration

2. Lead aprons and collars3. Intraoral technique: long – cone paralleling technique.4. Exposure Factors: hi kVp, lo kVp, mAs5. Processing

6. Quality assurance: equipment works properly, employees well trained.7. Image viewing: semi dark room, all extraneous lite eliminated, magnifying glass.8. Continuing Education.

7. What steps to protect dental office personnel?a. 1. Use the steps to reduce patient exposure

2. Barriers3. Operator at least 6 ft from patient at angle of 90-135 degrees to central beam.4. Patient management: use film holders; if patient needs assistance, non-

occupationally exposed person should help (i.e. parent).5. Tube head and suspension arms stable.6. Film badge to monitor amt. of radiation exposure to staff or work areas.

8. What are the parts of the film? a. Supercoat - Emulsion - Adhesive – Base – Adhesive - Emulsion – Supercoat

9. What is the function of each part?a. 1. Supercoat: protects emulsion

2. Emulsion: a. Gelatin: keeps AgX (silver halide) grains well dispersed; allows processing soln’s to penetrate w/o destroying it. b. Silver halide: Small crystals in gelatin gives photographic sensitivity; clumps of silver atoms formed from action of xrays on sensitized silver grains will be visible after developing process. c. Ionization process: makes the latent image (= pattern of information

formed on the film as the beam is attenuated by a patient).3. Adhesive: firmly attaches emulsion to base.4. Base: Support for the emulsion

10. What is a latent image and how is it formed?a. latent image = pattern of information formed on the film as the beam is attenuated by a patient. They are clumps of silver atoms formed due to action of light of xrays on sensitized silver iodo-bromide grains which will be visible after the developing process. Ionization process: makes the latent image.

11. What is difference btw/ non-screen and screen film?Non-screenIntraoral filmDirect: made to be sensitive to direct exposure of xrayMore resolution and sharp than indirect film (screen)Ultraspeed (D), Ektaspeed(E), F-speed

ScreenExtraoral (up to now)IndirectMore sensitive to light fluorescenceUsed w/ intensifying screens

Less resolution and sharpness than direct filmEach screen-film combo has own speed

12. What is the structure of intensifying screens? And functions of each layer?1. Protective layer – plastic2. Phosphor layer – give off light in response to xrays3. Reflecting coat – reflects light back toward front of screen4. Base – polyester plastic

13. What is the overall function o the intensifying screens?Emits light (fluoresce) when exposed to radiation; reduces patien exposure.

14. What are the types of intensifying screens? Which one preferred?Calcium tungstate; and rare earth (preferred b/c faster)

15. Define density?Amount of film blackness

16. Define Contrast?Difference in densitites btw/ different areas on a radiograph

17. What is low contrast? And high?Low contrast = many shades of grayHi contrast = few shades of gray

18. What is the characteristic curve?Graphically expresses density plotting exposure (mAs) and density.

19. What does higher slope on the characteristic curve mean?Greater film contrast.

20. What does film gamma mean?Maximum slope of the characteristic curve.

21. What is average gradient?Slope of a straight line joining the two points of specified density on charact. curve.

22. What is fog? What can cause fog?Development of unexposed silver halide grains. Improper film storage; improper safelight conditions; improper development (can cause fog).

23. What is speed?The reciprocal of the exposure required to produce a given density.

24. What controls the shape of the char. curve?

Film contrast.

25. What determines location of the curve on the log exposure scale?Film speed.

26. What is latitude?Rangeof log relative exposure (mAs) that will prod. density w/in the accepted diagnostic radiology range.

27. Film latitude is inversely or directly proportional to film contrast?Generally inverse.

28. In the diagram below, which has higher constrast A or B? Which has greater latitude?

A B

A has higher constrast b/c of the higher slope; B has greater latitude b/c of the longer range of mAs/log relative exposure (x axis) that will produce density (y axis) in the accepted range.

29. What is mottle?Mottle = noise = non-uniform density

30. What is sharpness? And list factors that influence it.Ability to define an edge (describes how well an edge is defined on the image; influenced by……

Geometric unsharpnessMotion unsharpnessAbsorption unsharpnessScreen unsharpnessParallax unsharpness

31. What is resolution?Ability to record separate images of small objects that are placed very closed together.Or (better rephrased) Describes the ability to perceive objects as separate entities.

32. How is resolution measured?In line pairs per mm that can be clearly seen on the film.

33. What is a grid?Alternating parallel strips of radiopaque mat’l (lead) and radiolucent mat’l (plastic);Used to reduce or remove scattered radiation exiting object b4 it reaches film; requires increased exposure.

34. What are the advantages of grids then?Decreased film fog/increased contrast

THE RADIOGRAPHIC IMAGE1. Projection geometry1. What are 3 reasons why radiographs display geometric characteristics? a. xrays originate from area rather than a point

b. xrays travel in str8 lines but along divergent pathways from source.c. anatomic structures: 3-D → recorded on 2-D medium

2. What is an umbra? Penumbra?Umbra: image or shadow of the actual object seen on film; Penumbra: area of unsharpness of the image

3. Explain how geometric principles affect radiographic image quality?a. xrays travel in str8 lines from all points on the surface of the xray source (focal spot).b. xrays pass thru anatomical object being examined.c. xrays form an image on film in relation to variable thickness of object forming an

umbra and penumbra.

4. What is the 1st rule to improve sharpness and resolution of image? How can we accomplish this rule?

Keep source as small as possible…..achieved by1. small focal spot2. minimal motion of source3. collimation

5. What is the 2nd rule to improve sharpness and resolution? How accomplished?Source-object distance great as possible…..achieved by using long cone rather than short cone.

6. What about the 3rd rule?Object-film distance as small as possible

7. In lower molar area how do we can accomplish the 3rd rule w/ the aid of what?Tongue

8. In the upper premolar and molar areas where should we keep the film?Closer to middle of arch.

9. What is magnification?Magnification = Size distortion = enlargement of actual size of object on the

radiographic image.

10. How to minimize mag?Increase source-film distance; decrease object-film distance.

11. How is it that calculation of magnification is possible?Theory of similar triangles → angles and therefore sides and altitudes proprortional.

12. What is shape distortion?Unequal magnification of the object on the radiograph.

13. How to minimize shape distortion?( Rule 4) Positioning film parallel to object/teeth; (Rule 5) orient central beam

perpendicular to objectand film.

14. What are 2 types of distortion and define them and how they it happens?a. foreshortening = image appears shorter than object

→ film is not parallel w/ object, central beam is perpendicular to film but not object.

b. elongation = image appears longer than object → film not parallel w/ object, central beam is perp. to object but not film.

15. To sum up what are the 5 rules of accurate film formation?1. Small radiation source2. Great source-object distance3. Small object-film distance4. Object and film parallel5. Source perpendicular to object and film.

2. Localization techniques1. To provide enhanced 3-D info. about the location of an object what 3 methods can we use?

a. right-angle methodb. tube shift rule c. buccal-object rule

2. What is the right-angle method?

2 projections made at right angles to each other (ie a periapical and an occlusal projection)

3. What is the tube shift rule? And what rule/guideline does it utilize?2 periapical projections with different horizontal angulatons.Utilizes the SLOB rule = same/lingual, opposite/buccal

4. What is the Buccal-object rule? And what guideline does it utilize also?2 periapical projections made w/ different horizontal or vertical angulations.SLOB also applies to vertical dimension

5. To calculate Magnification what 3 equations are equal to magnification and thus each other?M = D(source-film dist)/ d(source-object dist) = D/ D – ofd (object film distance) = I(image size)/ O(object size)

PROCESSING

1. Define development?Process that amplifies latent image by factor of millions to form a visible silver pattern.

3. What are the 5 Parts in developing solution?a. Developing solution: hydroquinone and elon(metol)b. Activator(accelerator): alkalic. Preservative: sodium sulfated. Restrainer: potassium bromidee. Solvent

4. What are the 2 components of developing soln. and which is temp. sensitive and their function? a.Hydroquinone: temperature sensitive (higher activity at higher temp); slowly builds

black tones (high contrast).b. Elon (metol): not temp. sensitive; quickly builds gray tones( low contrast).

5. What is the purpose of the activator?Softens emulsion and hastens reducing process.

6. What about the preservative?Protects reducing agents by decreasing rate of oxidation of reducing agent.

7. What about restrainer?

Decreases rate of fog formation from development of unexposed silver halide crystals.

8. What about solvent?Water; vehicle for solution that softens emulsification.

9. What is the purpose of replenishment of developing soln.?

Replenish lost developer and reduce effects of oxidation.

10. What is the purpose of Fixer?Unexposed and undeveloped crystals are removed from the emulsion w/o damaging

the image formed by metallic silver.11. What are the 5 components of Fixer?

a. Fixing solution (clearing agent): thiosulfateb. Acidifier: acetic acidc. Hardening Agent: Al or Cr Potassium sulfated. Preservative: sodium sulfatee. Solvent : functions to provide vehicle for chemicals.

12. Function of fixing soln.?Forms silver thiosulfate complexes from unexposed silver bromide crystals.

13. Function of acidifier?Neutralizes any remaining developer & provides acid medium for fixing solution

14. Function of Hardening agent?Prevents excessive swelling of emulsion & hardens emulsion (more resistance to

abrasion)

15. Function of preservative?Protects fixing soln/ clearing agent from oxidation. Maintains chem. Balance of fixer.

16. Since the fixing solution is Acidic what is the Developing solution?Alkaline

17. In the darkroom give the specifications for proper lighting?Block out white light; 4 ft above surface; 15watt bulb; GBX-2 filter (red).

18. What is the significance of time and temperature in the processing of radiographs?Time is based on temperature: they are inversely related: increase temp. reduce time to process(automatic and rapid processing);

19. What are the steps in automatic processing? Developer – fixer – water wash- drying

20. What does archival quality mean?

In rapid processing film must be completely fixed and washed to achieve archival (longlasting/permanency).

21. If a double film was not used and we want to make a copy of a radiograph, what do we do?Exposure of original onto special duplicate film w/ a single emulsion that forms a positive image.

22. T or F shorter exposure produces a darker duplicate; and longer exposure produces a lighter duplicate?TRUE